The preparaton of glasses in the system Si--Y--Al--O--N has been reported by several investigators. J.Am.CeramicSoc. 65 [8] C-123 (1982).
To form such glasses, powdered alumina, silicon nitride, silicon dioxide, and yttrium oxide are weighed and then mixed, as by tumbling in a plastic container. The powder mixture is then compacted by isostatic pressing to form pellets. These pellets are then loaded into boron nitride-lined crucibles. The powder mixture is then melted in a nitrogen atmosphere at 100 kPa. Typically, the melting temperature is in excess of 1600.degree. C., and the melting time required is two to four hours. The melt is furnace-cooled to room temperature as fast as is practicable, and, for large (&gt;50 g) batches, reheated to about 700.degree. C. for two hours for annealing.
The preferred raw materials, with the approximate preferred purity for each, are as follows. 99.995% Alpha Al.sub.2 O.sub.3, Gallard-Schlesinger Corp., Carle Place, N.Y.; AME CP 85 Si.sub.3 N.sub.4, Advanced Materials Engineering, Gateshead, Durham, U.K.; 99.5% high-purity fused SiO.sub.2, Thermo-Materials Corp., Atlanta, Ga., and 99.9% Y.sub.2 O.sub.3, Molycorp, N.Y.
Such glasses typically have high elastic moduli. These glasses also demonstrate an increase in glass hardness with increasing nitrogen content. Similarly, the glass transition temperature and viscosity increase with increasing nitrogen content.
All of these observations support the theory that the replacement of oxygen with nitrogen in the glass structure leads to a tightening of the glass network by means of the formation of more bonds than would be present in a similar oxide glass.
Previous investigations of such glasses have been confined to the production of cylindrical ingots and disks. The properties of these glasses have been investigated in part because of the recent developments in heat engine technology, which have stimulated interest in a variety of ceramic materials for high-temperature structural applications. Ceramic Eng. and Sci. Proc. 3, 565-576 (1982).